RM0090: Reference manual - STMicroelectronics

RM0090 General-purpose I/Os (GPIO)
Figure 20. Input floating/pull up/pull down configurations
Write
Read
Bit set/reset registers
Read/write
Output data register
7.3.10 Output configuration
TTL Schmitt
trigger
When the I/O port is programmed as output:
Input data register
input driver
output driver
● The output buffer is enabled:
– Open drain mode: A “0” in the Output register activates the N-MOS whereas a “1”
in the Output register leaves the port in Hi-Z (the P-MOS is never activated)
– Push-pull mode: A “0” in the Output register activates the N-MOS whereas a “1” in
the Output register activates the P-MOS
● The Schmitt trigger input is activated
● The weak pull-up and pull-down resistors are activated or not depending on the value in
the GPIOx_PUPDR register
● The data present on the I/O pin are sampled into the input data register every AHB1
clock cycle
● A read access to the input data register gets the I/O state
● A read access to the output data register gets the last written value
Figure 21 shows the output configuration of the I/O port bit.
on
VDD
VDD
on/off
protection
pull diode
up
I/O pin
on/off
pull
down
Doc ID 018909 Rev 3 194/1416
VSS
VSS
protection
diode
ai15940b